Patent GB-599435-A (GB)
Title: Means for controlling power transmissions utilizing an inverter
IPC: H02M7/51
Filed: 1944-10-25
Abstract: 599,435. Converting. ALLMANNA SVENSKA ELEKTRISKA AKTIEBOLAGET. Oct. 25, 1944, No. 20709. Convention date, Oct. 30, 1943. [Class 38 (ii)] A D.C. transmission line receives power at one end through a rectifier comprising a number of series connected units and delivers it through an inverter having grid control so regulated that it acts to keep the current constant when not overcome by another regulating action. Generally, the control will be set to keep the current lower than that determined by the other normal conditions, e.g. the rectifier may be fitted with a current controller. In such a case, the inverter regulator may be so constructed that it cannot reduce the current determined by the rectifier, but can raise the current if it falls below the set value, e.g. when back-arcing occurs in one rectifier unit. The Figure shows an inverter so controlled. Each of six converting vessels 1-6 may have a regulator such as is shown applied to the valve 4. The D.C. current passes through a. transductor 8 and varies the current supplied from an A.C. source 9 to a rectifier 10, the D.C. output from which is compared with a standard current from source 13 obtained as described, for example, in Specification 479,834, the difference current passing between points 11, 12 through winding 14 of another transductor. The inductance of winding 15 is thus varied to shift the phase of the supply to the grid of vessel 4 from the junction between inductance 15 and resistance 16 which are connected in series across a potentiometer 17. A unidirectional conductor 19 is connected in series with winding 14 so that while the grid potential may be varied to raise the main D.C. load current to a predetermined value, it cannot be varied to lower the D.C. load current. Regulation by winding 18 limits the phase displacement of the grid voltage to the region of safe commutation or is set to determine the D.C. voltage. Both rectifier and converter regulators may have an overriding voltage control which may be set so that under normal conditions the current may lie between the two set values. With inverter commutation failure, the rectifier controller limits the current. In starting up the transmission line from the inverter station, the inverter is connected to the line which is open-circuited at the rectifier end. Then the rectifier is connected so that its exciter current is supplied and controlled by the inverter acting as a rectifier, until the rectifier is connected fully to supply and control the current, while the inverter determines the voltage, its grid angle being limited either with respect to safe commutation or to some other value. The inverter current setting may be manually adjustable at the rectifier end and is normally set only just below the rectifier control value, but when starting after an interruption, is set quite low until the system reaches full voltage. The rectifier may be regulated by remote control from the inverter end when the load has reached the maximum allowable to the inverter, the control of which is correspondingly altered either upon telephoned instructions, or automatically. If the control setting is lowered, the speed of doing it should be slow.